Euclid

Abstract:

The rate at which galaxy halos form is thought to play a key role in explaining many observable cosmological phenomena such as the initial epoch at which luminous matter forms and the distribution of active galaxies. Here we show how Press-Schechter theory can be used to provide a simple, completely analytic model of the halo formation rate. This model shows good agreement with both Monte-Carlo and N-body simulation results.

Abstract:

We describe the new, fast, high-precision microdensitometer SuperCOSMOS. Some aspects of hardware and software design that enable high-precision astrometry from photographic plates are explained. We show that the positioning repeatability of the measuring machine is less than 0.1 μm standard error in either coordinate, and the absolute positional accuracy is about 0.15 μm standard error. Furthermore, measurements of the same plate in different orientations show that the sampling errors are small (e.g. ∼0.2 μm, rising to ∼1.0 μm at the plate limit, for stellar images in a IIIaJ emulsion), thus allowing the extraction of relative positional information from Schmidt plates at accuracies less than 1 μm. We demonstrate that SuperCOSMOS is capable of measuring the positions of bright stars (i.e. those more than ∼4 mag above the plate limit) to a precision ∼0.5 μm with survey-grade photographic plates employing fine-grained emulsions.